The present invention relates to pitch control of a rotor blade assembly, and more particularly to a rotor blade with a trailing edge flap driven by a servo flap that is offset relative to the trailing edge flap along the blade span wise direction.
Some rotary wing aircraft utilize servo flaps for pitch positioning of a main rotor blade. The servo flaps are often located aft of the trailing edges of their associated rotor blades. Such trailing edge servo flaps, in combination with their associated rotor blades, are essentially stable. That is, when the servo flap is moved about its own pitch axis, the blade moves (pitches) toward a balanced condition at which the aerodynamically induced pitch changing moment that is applied to the blade by the servo flap is opposed by the aerodynamic pitch changing moment experienced by the blade.
A major disadvantage of conventional servo flaps is that a relatively large servo flap is usually required to produce the forces and moments necessary to control the pitch of the main rotor blade. These servo flaps require powerful actuators, which may be relatively heavy and mechanically complex. Actuator size may also be a limitation as the actuators must be located within the restricted space inside the rotor blade. Otherwise, significant drag and power penalties accrue if the actuators are exposed to the airflow. Redundancy requirements and the necessity of connecting control armatures and linkages or transferring a motive fluid via hydraulics through a rotational interface to the actuator may further complicate conventional servo flap operation.
Accordingly, it is desirable to provide a rotor blade pitch control system utilizing an uncomplicated and lightweight trailing edge servo flap that requires minimal actuation force and a minimal transfer of a motive force through a rotational interface.